The current trend in telecommunications network evolution focuses on supplanting the traditional public switched telephone network (PSTN) with emerging packet-switched based data networks. There are a number of contributing factors to this trend. Data traffic volume has far exceeded voice traffic volume and the gap continues to grow unabated. Studies have shown that voice will constitute only a very small percentage of the total telecommunication traffic. Furthermore, a data network is inherently more flexible for supporting a variety of voice and data services and has the technical potential to support all the services that are carried over PSTN today.
It will take years before all technical issues are resolved so that data networks can have the superior quality and reliability of PSTN. Meanwhile, PSTN and the rapidly developing data networks will continue to coexist. To facilitate the migration of voice telephony from PSTN toward packet networks, and to make two networks interoperate for voice services, network operators are deploying voice media gateways. Voice media gateways convert voice signals between time division multiplex (TDM) pulse code modulation (PCM) and a data packet format, either asynchronous transfer mode (ATM) or voice over Internet protocol (VoIP). Therefore, voice media gateways are currently used to bridge the data network and the PSTN, but does not perform the necessary switching functions. This type of transition network, though necessary, is not economical since it introduces duplicative network elements and increases the cost of operating and maintaining the network.